1. The Field of the Invention
This invention relates to a method and apparatus for severing a sheet of refractory material and, more particularly, to sever the bulb edges of a sheet cut from a continuous glass ribbon.
2. Discussions of the Technical Difficulty
As taught in U.S. Pat. No. 3,998,616 in the manufacture of glass ribbon by the float method, a continuous ribbon of molten glass is controllably cooled as it moves through a forming chamber on a pool of molten metal. The edges of the molten glass are engaged by attenuating machines as the glass cools. The attenuating machines move the edges relative to one another to provide a dimensionally stable glass ribbon having a thickness other than equilibrium thickness. After sequentially exiting the forming chamber and annealing lehr, the glass ribbon is cut into sections normally called "lehr ends" or "caps". Since the outside edges of the lehr ends are deformed by earlier contact with the attenuating machines, the outermost portion known as "bulb edges" are not usable and must be removed.
It is known that the bulb edges to be removed can be scored at a scoring station where a score is imposed on the upper surface of the glass sheet adjacent to each of the bulb edges. Thereafter the prescored lehr end is momentarily halted at an edge snap roll in which a rigid member positioned above and along the bulb edge moves downward to snap the bulb edge from the lehr end. The glass sheet is supported by the conveyor.
In U.S. Pat. No. 3,303,980 an edge snapping device is disclosed in which an anvil is engaged with one surface (lower) of the glass sheet and a striker is engageable with the opposite (upper) surface of the sheet to provide an edge snap.
U.S. Pat. No. 3,779,437 discloses an edge cutting device which includes at least two cutter means and a breaking means.
U.S. Pat. No. 4,049,167 discloses a process for removing edge portions from a glass sheet in which a previously applied score line is hammered on the opposite side of the score and a bending force is applied to the sheet to initiate breakage.
In U.S. Pat. No. 4,285,451 a method and an apparatus for severing edges of a glass sheet is disclosed in which the surface of a resilient member lying in a plane subtending an oblique angle with the sheet is moved downward against the bulb edge to sequentially sever the bulb edge at a first and second score line previously applied.
U.S. Pat. No. 3,268,135 discloses a method and apparatus for snapping sheets of glass by applying a curvature on the sheet.
U.S. Pat. Nos. 4,109,841 and 4,136,807 disclose a method and apparatus for opening score lines in glass sheets by snapping the score with a bending moment applied to the glass sheet along a path transverse to the article movement path.
One of the problems associated with snapping the bulb edge portions along a score line is that the edge produced has defects, including serration hackle, chips, deep sharks teeth, flare and bevel, especially in glass sheets having a thickness greater than 5 mm. Although many automated bulb edge snapping machines do work well enough with thinner glass, the best edges on thicker glass sheets are obtained by hand cutting in which a score line is "run" to open the score by applying a bending moment to one end of the score line. Unfortunately, the use of hand cutting techniques on the main line of an automated float plant to sever bulb edges is not feasible. Accordingly, an apparatus is needed that will provide a good clean edge on lehr ends even on thicknesses of glass above 5 mm. The resultant edge should be of the quality of hand cutting techniques and yet be fully automated and capable of high speed operation with a quick recycling time. The instant invention is directed toward those needs.